Silane coatings for bonding rubber to metals

ABSTRACT

A method of treating a metal substrate by applying a coating of a silane composition having at least one substantially unhydrolyzed aminosilane having one or more secondary or tertiary amino groups. Methods of adhering a polymer (such as rubber) to a metal substrate are also provided.

RELATED APPLICATIONS

The present application is a Divisional of U.S. application Ser. No.09/356,912 filed Jul. 19, 1999 and issued on Jul. 9, 2002 as U.S. Pat.No. 6,416,869.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to silane coatings for metals. Moreparticularly, the present, invention provides silane coatings which notonly provide improved adhesion to rubber and other polymers, but alsoprovide corrosion protection (with or without a polymer layer).

2. Description of Related Art

Most metals are susceptible to corrosion, including the formation ofvarious types of rust. Such corrosion will significantly affect thequality of such metals, as well as that of the products producedtherefrom. Although rust and the like may often be removed, such stepsare costly and may further diminish the strength of the metal. Inaddition, when polymer coatings such as paints, adhesives or rubbers areapplied to the metals, corrosion may cause a loss of adhesion betweenthe polymer coating and the metal.

By way of example, metallic coated steel sheet such as galvanized steelis used in many industries, including the automotive, construction andappliance industries. In most cases, the galvanized steel is painted orotherwise coated with a polymer layer to achieve a durable andaesthetically-pleasing product. Galvanized steel, particularlyhot-dipped galvanized steel, however, often develops “white rust” duringstorage and shipment.

White rust (also called “wet-storage stain”) is typically caused bymoisture condensation on the surface of galvanized steel which reactswith the zinc coating. On products such as GALVALUME®, the wet-storagestain is black in color (“black rust”). White rust (as well as blackrust) is aesthetically unappealing and impairs the ability of thegalvanized steel to be painted or otherwise coated with a polymer. Thus,prior to such coating, the surface of the galvanized steel must bepretreated in order to remove the white rust and prevent its reformationbeneath the polymer layer. Various methods are currently employed to notonly prevent the formation of white rust during shipment and storage,but also to prevent the formation of white rust beneath a polymercoating (e.g., paint).

In order to prevent white rust on hot-dipped galvanized steel duringstorage and shipping, the surface of the steel is often passivated byforming a thin chromate film on the surface of the steel. While suchchromate coatings do provide resistance to the formation of white rust,chromium is highly toxic and environmentally undesirable. It is alsoknown to employ a phosphate conversion coating in conjunction with achromate rinse in order to improve paint adherence and provide corrosionprotection. It is believed that the chromate rinse covers the pores inthe phosphate coating, thereby improving the corrosion resistance andadhesion performance. Once again, however, it is highly desirable toeliminate the use of chromate altogether. Unfortunately, however, thephosphate conversion coating is generally not very effective without thechromate rinse.

Recently, various techniques for eliminating the use of chromate havebeen proposed. In particular, various silane coatings have beendeveloped for preventing corrosion of metal substrates. For example,U.S. Pat. No. 5,108,793 describes a technique of coating certain metalsubstrates with an inorganic silicate followed by treating the silicatecoating with an organofunctional silane (U.S. Pat. No. 5,108,793). U.S.Pat. No. 5,292,549 teaches the rinsing of metallic coated steel sheetwith a solution containing an organic silane and a crosslinking agent.Other silane coatings are described in U.S. Pat. Nos. 5,750,197 and5,759,629, both of which are incorporated herein by way of reference.

Often, the corrosion protection provided by a particular silane coatingwill depend upon the identity of the metal substrate itself. Inaddition, the silane coating must also be compatible with any polymerlayer to be applied over the silane coating (such as paints, adhesivesor rubbers). For example, while a particular silane coating may provideexcellent paint adhesion and corrosion protection, that same silanecoating may provide little or no adhesion to certain rubbers. Thus, itis often necessary to tailor the silane coating to the specificapplication.

The silane coatings (or films) known heretofore are typically appliedfrom an aqueous solution wherein the silane(s) are at least partiallyhydrolyzed. The resulting silane films, however, often contain residualwater that can only be driven out by a high temperature heat treatment.Although the films are usually somewhat crosslinked, higher degrees ofcrosslinking typically require high temperature heat treatment (e.g.,200° C.). These silane films are often very thin and fragile, and nevercompletely pore-free or impervious to water. Therefore, corrosion maystill occur to some extent when silane coated metals are exposed to ahumid environment for a lengthy period of time. While high temperatureheat treatment may help alleviate some of these problems, hightemperature heat treatment may not always be practical. Thus, there is aneed for a silane coating having improved mechanical properties andhigher crosslink density, without the need for high temperatureprocessing.

In addition to corrosion prevention, adhesive bonding between metals andrubber is also of interest. For example, many automobile components(such as tire cords and vibration dampers) rely on adhesive bondingbetween a metal substrate and a sulfur-cured rubber. Steel tire cords,for example, are typically coated with a thin layer of brass in order topromote adhesion between the underlying steel and the sulfur-curedrubber. In addition, adhesion promoters such as cobalt salt additives,and HRH systems (hexamethylene tetramine, resorcinol and hydratedsilica) are also used to further enhance rubber adhesion for tire cords.Solvent-based adhesive systems are used in other applications forbonding metals to sulfur-cured rubbers. Although the performance of thevarious methods currently employed is adequate, they still suffer fromseveral drawbacks. Cobalt salts, for example, are expensive and poseavailability problems, while brass stimulates galvanic corrosion inconjunction with steel. Solvent-based adhesives are flammable and hencehazardous.

Although certain silanes have been found to promote adhesion between ametal substrate and a polymer layer, the results are typically systemdependent. In other words, the amount of adhesion provided by aparticular silane coating typically depends on the metal substrate aswell as the polymer layer to be adhered thereto. For example, whilecertain silane solutions may provide improved adhesion between a metalsubstrate and a peroxide-cured rubber, these same silane solutions willoften not provide the same results for sulfur-cured rubber. Thus, thereis also a need for methods of improving the adhesion between a metalsubstrate and a polymer layer, particularly sulfur-cured rubber.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide silane coatings on ametal substrates for improving corrosion resistance and/or polymeradhesion.

It is another object of the present invention to provide silane coatingswhich provide improved adhesion to rubber, including sulfur-cured andperoxide-cured rubber.

The foregoing objects, in accordance with one aspect of the presentinvention, are provided by a method of treating a metal substrate,comprising:

(a) providing a metal substrate; and

(b) applying a coating of a silane composition onto the metal substrate,the silane composition comprising at least one substantiallyunhydrolyzed aminosilane which has one or more secondary or tertiaryamino groups.

Suitable aminosilanes include:

wherein:

n is either 1 or 2;

y=(2−n);

each R¹ is individually chosen from the group consisting of: C₁-C₂₄alkyl and C₂-C₂₄ acyl;

each R² is individually chosen from the group consisting of: substitutedaliphatic groups, unsubstituted aliphatic groups, substituted aromaticgroups, and unsubstituted aromatic groups;

R⁵ is chosen from the group consisting of: hydrogen, C₁-C₁₀ alkylene,C₁-C₁₀ alkylene substituted with one or more amino groups, C₁-C₁₀alkenylene, C₁-C₁₀ alkenylene substituted with one or more amino groups,arylene, and alkylarylene;

X is either:

wherein each R³ is individually chosen from the group consisting of:hydrogen, substituted and unsubstituted aliphatic groups, andsubstituted and unsubstituted aromatic groups; and

R⁴ is chosen from the group consisting of: substituted and unsubstitutedaliphatic groups, and substituted and unsubstituted aromatic groups; and

wherein, when n=1, at least one of the R³ and the R⁵ is not hydrogen(else the aminosilane would contain no secondary or tertiary aminogroup).

Particularly preferred aminosilanes include bis-silyl aminosilaneshaving two trisubstituted silyl groups, wherein the substituents areindividually chosen from the group consisting of alkoxy, aryloxy andacyloxy. Suitable bis-silyl aminosilanes include:

wherein:

each R¹ is individually chosen from the group consisting of: C₁-C₂₄alkyl and C₂-C₂₄ acyl;

each R² is individually chosen from the group consisting of: substitutedaliphatic groups, unsubstituted aliphatic groups, substituted aromaticgroups, and unsubstituted aromatic groups; and

X is either:

wherein each R³ is individually chosen from the group consisting of:hydrogen, substituted and unsubstituted aliphatic groups, andsubstituted and unsubstituted aromatic groups; and

R⁴ is chosen from the group consisting of: substituted and unsubstitutedaliphatic groups, and substituted and unsubstituted aromatic groups.

Exemplary bis-silyl aminosilanes include:bis-(trimethoxysilylpropyl)amine, bis-(triethoxysilylpropyl)amine,bis-(triethoxysilylpropyl)ethylene diamine,N-[2-(vinylbenzylamino)ethyl]-3-aminopropyltrimethoxy silane, andaminoethyl-aminopropyltrimethoxy silane.

Although the coating provided by the unhydrolyzed aminosilanecomposition provides improved corrosion protection, the composition mayfurther include at least one “other” substantially unhydrolyzed silane(i.e., an unhydrolyzed silane other than an aminosilane having at leastone secondary or tertiary amino group). In particular, organofunctionalsilanes such as at least one substantially unhydrolyzed bis-silylpolysulfur silaine, may be included in order to provide improvedadhesion to a polymer (such as a paint, an adhesive, or a rubber,including sulfur-cured rubber). Suitable “other” silanes includebis-silyl polysulfur silanes comprising:

wherein each R¹ is an alkyl or an acetyl group, and Z is —Q—S_(x)—Q—,wherein each Q is an aliphatic or aromatic group, and x is an integer offrom 2 to 10. An exemplary bis-silyl polysulfur silane isbis-(triethoxysilylpropyl) tetrasulfide.

In one preferred embodiment, one or more substantially unhydrolyzedbis-silyl aminosilanes are combined with one or more substantiallyunhydrolyzed bis-silyl polysulfur silanes to provide a silanecomposition which may be applied to a metal substrate. The resultantsilane coating not only provides corrosion protection (even without apolymer coating thereover), but also provides surprisingly improvedadhesion to polymers such as paints, adhesives, and rubbers. Inparticular, the silane coating provides improved adhesion tosulfur-cured rubbers, as well as peroxide-cured rubbers. Uncured (oreven cured) rubber compounds are simply applied directly on the silanecoating, and then cured in the usual fashion (or, if already cured, therubber is simply heated while applying pressure). Sulfur-cured andperoxideured rubber compounds known to those skilled in the art may beadhered to metal substrates in this manner, using standard rubber curingmethods also known to those skilled in the art.

The above mixture of one or more bis-silyl aminosilanes and one ore morebis-silyl polysulfur silanes may also be provided as a partially orsubstantially hydrolyzed silane solution. This hydrolyzed silanesolution also provides surprising adhesion to polymers, particularlysulfur-cured and peroxide-cured rubbers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In U.S. Pat. No. 5,750,197, it was demonstrated that an aqueous solutionof a hydrolyzed bis-functional silane (such as1,2-bis-(trimethoxysilylpropyl)amine) provides corrosion protection.Applicants have now found that mixtures of at least one aminosilane andat least one bis-silyl polysulfur silane provide further improvements inboth corrosion protection and polymer adhesion (particularly tosulfur-cured rubber). The silanes do not have to be hydrolyzed, aspreviously believed, since these silane mixtures provide corrosionprotection and enhanced polymer adhesion whether hydrolyzed orunhydrolyzed. In addition, one or more unhydrolyzed aminosilanes mayeven be applied to a metal substrate alone (with or without the additionof other silanes), since applicants have found that silane coatingsapplied in this manner will form a dry film which provides corrosionprotection. It is believed that secondary or tertiary amino groups inthe aminosilane will crosslink, even if the aminosilane has not beenhydrolyzed, thereby allowing the formation of a dry film from a one ormore unhydrolyzed silanes.

The solutions and methods of the present invention may be used on avariety of metals, including (but not limited to):

zinc and zinc alloys, such as titanium-zinc (zinc which has a very smallamount of titanium added thereto), zinc-nickel alloy (typically about 5%to about 13% nickel content), and zinc-cobalt alloy (typically about 1%cobalt);

metal substrates having a zinc-containing coating, such as galvanizedsteel (especially hot dipped galvanized steel (“HDG”) andelectrogalvanized steel (“EGS”)), GALVALUME® (a 55%-Al/43.4%-Zn/1.6%-Sialloy coated sheet steel manufactured and sold, for example, byBethlehem Steel Corp), GALFAN® (a 5%-Al/95%-Zn alloy coated sheet steelmanufactured and sold by Weirton Steel Corp., of Weirton, WV),galvanneal (annealed hot dipped galvanized steel) and similar types ofcoated metals;

steel, particularly cold rolled steel and carbon steel;

aluminum and aluminum alloys;

copper and copper alloys, such as brass; and

tin and tin alloys, including metal substrates (such as CRS) havingtin-containing coatings

The silane solutions and mixtures of the present invention may beapplied to the metal prior to shipment to the end-user, and providecorrosion protection during shipment and storage. The coated metal maybe used as is, or, more preferably the end user may apply a polymerlayer (such as paint, rubber, or adhesive) directly on top of the silanecoating in the usual manner. The silane coatings of the presentinvention not only provide excellent corrosion protection, but alsoprovide superior adhesion between the metal substrate and the polymerlayer. These silane coatings (or films) are also very durable and highlydeformable, and therefore provide significant corrosion protection evenafter deep drawing of the coated metal. The methods and compositions ofthe present invention are particularly useful for bonding metals torubber, including sulfur-cured rubber. In fact, the present inventionprovides improved adhesion between metals and sulfur-cured rubberwithout the need for cobalt adhesion promoters in the rubbercomposition.

The silane compositions of the present invention comprise one or moreaminosilanes and one or more bis-silyl polysulfur silanes. The solutionsdo not require the use or addition of silicates or aluminates, andeliminate the need for phosphate conversion coatings. The silanes in thetreatment solution may be substantially unhydrolyzed, partiallyhydrolyzed, or substantially fully hydrolyzed. As used herein, the term“substantially unhydrolyzed” simply means that the silane(s) are appliedeither in a pure state (no added solvents) or from a solution which doesnot include water. However, it is recognized that such silane(s) mayabsorb some water from the atmosphere, hence the term “substantiallyunhydrolyzed” (water is not purposefully added to the silane(s)).

The silane solutions of the present invention may also comprise one ormore substantially unhydrolyzed aminosilanes having at least onesecondary or tertiary amino group, with or without additional silanes ornon-aqueous solvents. Applicants have found that these unhydrolyzedaminosilanes will dry to a hard film at room temperature (typically in30 minutes or less. The silane coating applied from one or moreunhydrolyzed aminosilanes will readily crosslink, and will evencrosslink other silanes which are included in the coating. This findingis quite surprising, since conventional wisdom suggests that silanesshould only be applied to metals in a hydrolyzed state (i.e., from asolution which includes water).

Hydrolyzed Silane Solutions

The hydrolyzed silane solutions of the present invention preferablycomprise one or more bis-silyl aminosilanes and one or more bis-silylpolysulfur silanes. These hydrolyzed silane solutions also preferablyinclude water (for hydrolysis), and one or more compatible solvents(such as ethanol, methanol, propanol or isopropanol) in order tosolubilize the polysulfur silane. The amount of solvent employed willdepend upon the concentration of polysulfur silane(s) in the solution,and the solution should therefore include sufficient solvent tosolubilize the polysulfur silane(s). The ratio of water to solvent inthe silane solution (as applied to the metal substrate, by volume) maybe between about 1:99 and about 99:1, more preferably between about 1:1and about 1:20.

It is preferred (but not required) that the two silanes (bis-silylaminosilane and bis-silyl polysulfur silane) are hydrolyzed separatelybefore being mixed with one another to form the silane solution which isapplied to the metal substrate. Thus, one or more bis-silyl aminosilanesmay be hydrolyzed by mixing the silane(s) with water at the desiredconcentration. A compatible solvent (such as an alcohol) may be added asdesired, however hydrolysis of the bis-silyl aminosilane will generallyproceed to completion without an added solvent (and the resultinghydrolyzed silane solution will remain stable). One or more bis-silylpolysulfur silanes may be hydrolyzed in a similar fashion, however acompatible solvent should be included since these silanes are generallynot water-soluble. Thus, hydrolysis of the bis-silyl polysulfursilane(s) may take place in a solution having a water to solvent ratio(by volume) of between about 1:99 and about 99:1, more preferablybetween about 1:1 and about 1:20.

As an alterative to employing an organic solvent, the hydrolyzed silanes(particularly the polysulfur silane(s)) may be prepared as an emulsionwithout a solvent. The silane(s) is simply mixed with water and asuitable surfactant known to those skilled in the art. An emulsified,hydrolyzed solution of a bis-silyl polysulfur silane can be prepared,for example, by mixing a 5% solution of the silane in water along with0.2% of a surfactant (by volume). Suitable surfactants include, forexample, sorbitan fatty acid esters (such as Span 20, available from ICISurfactants). Once the emulsion of polysulfur silane has been prepared,it may simply be mixed with one or more hydrolyzed bis-silylaminosilanes as described below and then applied to the metal substrate.

During hydrolysis, the —OR¹ groups in the bis-silyl aminosilane(s) andthe bis-silyl polysulfur silane(s) (as defined below) are replaced byhydroxyl groups. In order to accelerate silane hydrolysis and avoidsilane condensation during hydrolysis, the pH may be maintained belowabout 10, more preferably between about 4 and about 9 (particularly forhydrolysis of the bis-silyl aminosilane). The pH ranges preferred duringsolution preparation should not be confused with the application pH(i.e., the pH of the silane solution applied to the metal substrate).The pH may be adjusted, for example, by the addition of one or morecompatible acids, preferably organic acids such as acetic, formic,propionic or iso-propionic. Sodium hydroxide (or other compatible base)may be used, if needed, to raise the pH of the silane solution. Somesilanes provide an acidic pH when mixed with water alone, and for thesesilanes pH adjustment may not be needed to accelerate silane hydrolysis.The individual silane solutions are preferably stirred for at least 24hours to ensure complete hydrolysis. In the case of the solution ofbis-silyl polysulfur silane(s), hydrolysis may be allowed to proceed forseveral days (such as 3-4 days, or more) for optimal performance. Oncethe individual silane solutions have been separately hydrolyzed, theyare mixed with one another prior to application on the metal substrate.The hydrolyzed silane mixtures, however, are stable for at least up to30 days, and therefore need not be used immediately after mixing.

It should be noted that the various silane concentrations discussed andclaimed herein are all defined in terms of the ratio between the amount(by volume) of unhydrolyzed silane(s) employed to prepare the treatmentsolution (i.e., prior to hydrolyzation), and the total volume oftreatment solution components (i.e., aminosilanes, polysulfur silanes,water, optional solvents and optional pH adjusting agents). In the caseof aminosilane(s), the concentrations herein (unless otherwisespecified) refer to the total amount of unhydrolyzed aminosilanesemployed, since multiple aminosilanes may optionally be present. Thepolysulfur silane(s) concentrations herein are defined in the samemanner. During preparation of the individual hydrolyzed silanesolutions, the silane concentration in each may vary significantly fromthe desired total silane concentration in the mixed silane solution(i.e., the solution which is applied to the metal substrate). It ispreferred, however, that the silane concentration in the individualhydrolyzed solutions is approximately the same as the desired totalsilane concentration in the mixed silane solution in order to simplifythe final mixing step. In this manner, the final mixed silane solutionmay be prepared simply by mixing the appropriate ratio of the individualsilane solutions.

As for the concentration of hydrolyzed silanes in the final, mixedsilane solution (i.e., the solution applied to the metal substrate)beneficial results will be obtained over a wide range of silaneconcentrations and ratios. It is preferred, however, that the hydrolyzedsolution have at least about 0.1% silanes by volume, wherein thisconcentration refers to the total concentration of bis-silylaminosilane(s) and bis-silyl polysulfur silane(s) in the solution. Morepreferably, the solution has between about 0.1% and about 10% silanes byvolume. As for the ratio of bis-silyl aminosilane(s) to bis-silylpolysulfur silane(s) in the hydrolyzed silane solution, a wide range ofsilane ratios provide beneficial results. Preferably, however the ratioof bis-silyl aminosilane(s) to bis-silyl polysulfur silane(s) is betweenabout 1:99 and about 99:1. More preferably, particularly when thehydrolyzed silane solution is to be used for rubber bonding, this ratiois between about 1:10 and about 10:1. Even more preferably, this ratiois between about 1:3 and about 3:1.

The term “application pH” refers to the pH of the silane solution whenit is applied to the metal surface, and may be the same as, or differentfrom the pH during solution preparation. When used to improve theadhesion of a rubber (particularly sulfur-cured rubber) to a metal, theapplication pH is preferably between about 4 and about 7, mostpreferably between about 4 and about 5. The pH of the mixed silanesolution may be adjusted in the manner described previously.

The metal surface to be coated with the mixed hydrolyzed silane solutionof the present invention may be solvent and/or alkaline cleaned bytechniques well-known to those skilled in the art prior to applicationof the silane solution. The hydrolyzed silane solution (prepared in themanner described above) is applied to the metal surface (i.e., the sheetis coated with the silane solution) by, for example, dipping the metalinto the solution (also referred to as rinsing), spraying the solutiononto the surface of the metal, or even brushing or wiping the solutiononto the metal surface. Various other application techniques well-knownto those skilled in the art may also be used. When the preferredapplication method of dipping is employed, the duration of dipping isnot critical, as it generally does not significantly affect theresulting film thickness. It is merely preferred that whateverapplication method is used, the contact time should be sufficient toensure complete coating of the metal (such as 10 seconds or more).

After coating with the silane solution of the present invention, themetal substrate may simply be air-dried at room temperature. Heateddrying is not preferred if the hydrolyzed silane coating is to be usedfor improving rubber adhesion, since it is preferred that the coatingremain only partially crosslinked. While heated drying (or curing)promotes crosslinking, too much crosslinking in the silane coating mayprevent sufficient adhesion between a rubber and the metal substrate. Ofcourse the amount of crosslinking can be tailored to suit one'sparticular needs (such as the desired bond strength between the metalsubstrate and rubber), and the present invention is therefore notlimited to silane coatings dried only at room temperature. Once dried,the treated metal may be shipped to an end-user, or even stored forlater use.

The coatings applied from hydrolyzed silane solutions of the presentinvention provide significant corrosion resistance during both shippingand storage. More importantly, this silane coating need not be removedprior to application of a polymer layer on top of the silane coating.Thus, the end-user, such as an automotive manufacturer, may apply apolymer (such as a paint, an adhesive or rubber) directly on top of thesilane coating without additional treatment (such as the application ofchromates or the use of solvent-based adhesives). The hydrolyzed silanecoatings of the present invention not only provide a surprisingly highdegree of adhesion to the polymer layer, but also prevent delaminationand underpaint corrosion even if a portion of the base metal is exposedto the atmosphere.

As reported in application Ser. No. 09/356,927, titled Silane Treatmentfor Electrocoated Metals, which names Wim J. van Ooij and Guru P.Sundararajan as inventors, and was filed on Jul. 19, 1999, and thedisclosure of which is incorporated herein by way of reference, thehydrolyzed silane solutions of the present invention having both abis-silyl aminosilane and a bis-silyl polysulfur silane also provideexcellent adhesion to paints (particularly electrocoats) and otherpolymeric adhesives. As also reported therein, and as incorporatedherein by way of reference, the hydrolyzed silane solutions of thepresent application also provide improved corrosion protection, as wellas adhesion to other non-rubber polymers (such as paints and adhesives).

The hydrolyzed silane coatings of the present invention are particularlyuseful for bonding rubber to various metal substrates, particularlysulfur-cured rubbers such as natural rubber (“NR”), NBR, SBR and EPDMcompounds. The uncured rubber compound is merely applied directly on topof the silane coating, and is then cured in the typical fashion (i.e.,using the cure conditions required for the particular rubber compoundemployed). Even previously cured rubber may be adhered to the metalsusing the silane coatings of the present invention simply by applyingthe cured rubber compound directly on top of the silane coating andthereafter applying sufficient heat and pressure to adhere the rubber tosilane coating (and hence to the metal substrate). Thus, the silanecoatings provided by the hydrolyzed silane solutions of the presentinvention provide improved rubber adhesion, as well as significantcorrosion protection. These results are surprising since a coatingapplied from a solution of a hydrolyzed bis-silyl aminosilane aloneprovides no adhesion to sulfur-cured rubber. Yet, when a solutioncomprising the same bis-silyl aminosilane and a hydrolyzed bis-silylpolysulfur silane is used, the resulting adhesion exceeds that providedby the bis-silyl polysulfur silane alone. Previously reported silanecoatings which provide improved adhesion to peroxide-cured rubbers,likewise provide no adhesion to sulfur-cured rubbers. An added benefitof the improved adhesion provided by the hydrolyzed silane coatings ofthe present invention is that the sulfur-cured rubbers may be formulatedwithout cobalt adhesion promoters, since the silane coatings of thepresent invention improve rubber adhesion without such promoters.

Since the hydrolyzed silane coatings of the present invention alsoprovide corrosion protection and bonding to polymers other than rubber(such as paint), the present invention has the added benefit ofproviding silane solutions and methods which may be used in a myriad ofapplications. Thus, manufacturers need not use one silane solution forcorrosion protection, another for paint adhesion, yet another foradhesion to peroxide-cured rubber, and still another for adhesion tosulfurcured rubber. The hydrolyzed silane solutions of the presentinvention are suitable for all of these applications on a variety ofmetals.

The preferred bis-silyl aminosilanes which may be employed in thepresent invention have two trisubstituted silyl groups, wherein thesubstituents are individually chosen from the group consisting ofalkoxy, aryloxy and acyloxy. Thus, these bis-silyl aminosilanes have thegeneral structure:

wherein each R¹ is chosen from the group consisting of: C₁-C₂₄ alkyl(preferably C₁-C₆ alkyl), and C₂-C₂₄ acyl (preferably C₂-C₄ acyl). EachR¹ may be the same or different, however, in the hydrolyzed silanesolutions of the present invention, at least a portion (and preferablyall or substantially all) of the R¹ groups are replaced by a hydrogenatom. Preferably, each R¹ is individually chosen from the groupconsisting of: ethyl, methyl, propyl, iso-propyl, butyl, iso-butyl,sec-butyl, ter-butyl and acetyl.

Each R² in the aminosilane(s) may be a substituted or unsubstitutedaliphatic group, or a substituted or unsubstituted aromatic group, andeach R² may be the same or different. Preferably, each R² is chosen fromthe group consisting of: C₁-C₁₀ alkylene, C₁-C₁₀ alkenylene, arylene,and alkylarylene. More preferably, each R² is a C₁-C₁₀ alkylene(particularly propylene).

X may be:

wherein each R³ may be a hydrogen, a substituted or unsubstitutedaliphatic group, or a substituted or unsubstituted aromatic group, andeach R³ may be the same or different. Preferably, each R³ is chosen fromthe group consisting of hydrogen, C₁-C₆ alkyl and C₁-C₆ alkenyl. Morepreferably, each R³ is a hydrogen atom.

Finally, R⁴ in the aminosilane(s) may be a substituted or unsubstitutedaliphatic group, or a substituted or unsubstituted aromatic group.Preferably, R⁴ is chosen from the group consisting of: C₁-C₁₀ alkylene,C₁-C₁₀ alkenylene, arylene, and alkylarylene. More preferably, R⁴ is aC₁-C₁₀ alkylene (particularly ethylene).

Exemplary preferred bis-silyl aminosilanes which may be used in thepresent invention include:

bis-(trimethoxysilylpropyl)amine (which is sold under the tradenameA-1170 by Witco):

bis-(triethoxysilylpropyl)amine:

and bis-(triethoxysilylpropyl)ethylene diamine:

The preferred bis-silyl polysulfur silanes which may be employed in thepresent invention include:

wherein each R¹ is as described before. In the hydrolyzed silanesolutions of the present invention, at least a portion (and preferablyall or substantially all) of the R¹ groups are replaced by a hydrogenatom. Z is —Q—S_(x)—Q—, wherein each Q is an aliphatic (saturated orunsaturated) or aromatic group, and x is an integer of from 2 to 10. Qwithin the bis-functional polysulfur silane can be the same ordifferent. In a preferred embodiment, each Q is individually chosen fromthe group consisting of: C₁-C₆ alkyl (linear or branched), C₁-C₆ alkenyl(linear or branched), C₁-C₆ alkyl substituted with one or more aminogroups, C₁-C₆ alkenyl substituted with one or more amino groups, benzyl,and benzyl substituted with C₁-C₆ alkyl.

Particularly preferred bis-silyl polysulfur silanes includebis-(triethoxysilylpropyl) sulfides having 2 to 10 sulfur atoms. Suchcompounds have the following formula:

wherein x is an integer of from 2 to 10. One particularly preferredcompound is bis-(triethoxysilylpropyl) tetrasulfide (also referred to asbis-(triethoxysilylpropyl) sulfane, or “TESPT”). Commercially-availableforms of TESPT (such as A-1289, available from Witco) , however, areactually mixtures of bis-(triethoxysilylpropyl) sulfides having 2 to 10sulfur atoms. In other words, these commercially-available forms ofTESPT have a distribution of sulfide chain lengths, with the S₃ and S₄sulfides predominating. Thus, the scope of the present inventionincludes hydrolyzed silane solutions containing mixtures of bis-silylpolysulfur silanes in combination with one or more bis-silylaminosilanes.

Coatings Applied from Unhydrolyzed Silanes

Applicants have also surprisingly found that unhydrolyzed silanes may beapplied directly onto the metal substrate in order to not only providecorrosion protection, but also to provide improved adhesion to polymerlayers (such as paints, adhesives, or rubbers). Preferably, at least oneaminosilane having at least one secondary or tertiary amino group (suchas the bis-silyl aminosilanes described above) is applied to the metalsubstrate in a substantially unhydrolyzed state (i.e., the R¹ groups arenot replaced by a hydrogen atom). One or more additional silanes(organofunctional or non-organofunctional) may also be mixed with theaminosilane, however even an unhydrolyzed aminosilane by itself providescorrosion protection.

The aminosilanes which may be applied to a metal substrate in anunhydrolyzed state include aminosilanes having at least one secondary ortertiary amino group. Suitable unhydrolyzed aminosilanes include:

wherein n is either 1 or 2. Thus, when a bis-silyl aminosilane of thetype described previously is employed, n=2. Each R¹ is as definedpreviously, each R² is as described previously, and X is as describedpreviously. R⁵ may be hydrogen, C₁-C₁₀ alkylene, C₁-C₁₀ alkylenesubstituted with one or more amino groups, C₁-C₁₀ alkenylene, C₁-C₁₀alkenylene substituted with one or more amino groups, arylene, andalkylarylene. When n=1, R³ and R⁵ should not all be hydrogen (else theaminosilane will have no secondary or tertiary aminosilane groups).Particularly preferred aminosilanes include the bis-silyl aminosilanes(i.e., n=2, y=0) described previously, as well as diamino silanes.Suitable diaminosilanes included those silanes having at least onetrialkoxysilyl or triacetoxysilyl group, as well as two amino groups, atleast one of which is a secondary amino group. Suitable diamino silanesinclude N-[2-(vinylbenzylamino)ethyl]-3-aminopropyltrimethoxy (“SAAPS”),aminoethyl-aminopropyltrimethoxy silane (“AEPS”), andbis-(triethoxysilylpropyl)ethylene diamine (a bis-silyl, diaminosilane).

The unhydrolyzed secondary or tertiary aminosilane(s) may also becombined with one or more additional unhydrolyzed silanes, particularlyorganofunctional silanes, prior to application to the metal substrate.In this fashion, one can tailor the silane coating to the particularapplication. While one or more unhydrolyzed secondary or tertiaryaminosilane(s) will provide a durable, corrosion-preventing film,applicants have found that the addition of one or more otherunhydrolyzed silanes (particularly organofunctional silanes, such asbis-silyl polysulfur silanes), will not only provide corrosionresistance but also polymer adhesion. “Organofunctional silane” simplymeans a silane having one or more trisubstituted silyl groups, and oneor more organofunctional groups.

One preferred embodiment of the present invention comprises a mixture ofone or more aminosilanes having at least one secondary or tertiary aminogroup (especially the bis-silyl aminosilanes described previously) andone or more bis-silyl polysulfur silanes (as described above), with thesilanes in a substantially unhydrolyzed state. The silane(s) (whether anaminosilane by itself, or a mixture of one or more aminosilanes and oneor more other silanes) may be applied to the metal substrate as a puresilane mixture (i.e., no solvents or water), or may be diluted with acompatible solvent (other than water). Suitable solvents, for example,include, ethanol, methanol, propanol and isopropanol. Diluting theunhydrolyzed silane(s) with a compatible solvent allows the thickness ofthe silane to be controlled.

The unhydrolyzed silane(s) are simply coated onto the metal substrate,such as by wiping, dipping or spraying the silane (or silane mixture)onto the metal. Thereafter, the silane coating is dried. If theunhydrolyzed silane mixture applied to the metal substrate contains onlyaminosilanes, the coating is preferably dried at room temperature.Alternatively, the aminosilane coating may be dried by heating to atemperature of between about 100° and about 250° for a period of timesufficient to form a dry film (i.e., silane coating).

When the unhydrolyzed silane mixture applied to the metal substrateincludes both an aminosilane (such as a bis-silyl aminosilane) and anorganofunctional silane (such as a bis-silyl polysulfur silane), thesilane coating is preferably dried by heating the coated metal to atemperature of between about 100° C. and about 250° C. (more preferablyto a temperature of between about 100° C. and about 160° C., for aperiod of time sufficient to form a dry film (such as about 10 to about60 minutes). It should be noted, however, that the amount of drying timewill obviously vary with the drying temperature, as well as the natureof the silane coating (e.g., silane concentrations, amount of organicsolvent, etc.). Thus, longer periods of time than that specified may beused. As the coating dries, the unhydrolyzed silanes will becomepartially crosslinked, thereby forming a semi-crosslinked silane coatingwhich not only provides significant corrosion protection, but alsoimproved adhesion to polymers such as paints, adhesives and rubbers(particularly sulfur-cured rubbers). When the unhydrolyzed silanecoating is used for polymer adhesion (particularly to sulfur-curedrubber), the silane coated metal should merely be dried for a period oftime sufficient to form a dry film (i.e., so that the silane film issemi-crosslinked). When the silane film is intended to provide corrosionprotection only, the silane film may be fully crosslinked (or cured)simply by heating the silane coated metal substrate for a longer periodof time and/or at a higher temperature. While a fully crosslinked silanefilm is not desired for polymer adhesion, it will provide significantcorrosion protection.

The unhydrolyzed silane mixtures of the present invention are preparedsimply by mixing the silanes with one another in their pure,unhydrolyzed state in the desired ratio. The resulting silane mixturemay be diluted with a compatible solvent, if desired. If a solvent isused, the total silane concentration should be at least about 10% (byvolume), more preferably at least about 25%.

As for the ratio of unhydrolyzed aminosilane(s) having at least onesecondary or tertiary amino group (such as unhydrolyzed bis-silylaminosilane(s)) to other unhydrolyzed silane(s) (such as unhydrolyzedbis-silyl polysulfur silane(s)), a wide range of silane ratios providebeneficial results. Preferably, however the ratio of aminosilane(s) toother silanes is between about 1:10 and about 10:1. More preferably,particularly when the unhydrolyzed silane mixture is to be used forrubber bonding, this ratio is between about 1:3 and about 1:1.

Applicants have found that unhydrolyzed silane compositions having atleast one secondary or tertiary aminosilane (particularly at least onebis-silyl aminosilane) provide a silane coating which is highlyresistant to corrosion. When the silane compositions include one or moreorganofunctional silanes (particularly at least one bis-silyl polysulfursilane), the resultant silane coating provides superior adhesion topolymers (such as paints, adhesives and rubbers). In fact, the adhesionto sulfur-cured rubbers is even greater than that provided by thehydrolyzed silane solutions of the present invention. Like thehydrolyzed silane solutions discussed previously, the unhydrolyzedsilane compositions of the present invention provide unexpectedly highlevels of adhesion to a variety of rubber compositions, includingsulfur-cured rubber such as high-sulfur rubber systems, low-sulfurrubber systems, EV rubber systems, and semi-EV rubber systems.

The coatings provided by the unhydrolyzed silane compositions of thepresent invention are also highly stable. Therefore, a polymer layer maybe applied long after the silane coating is established on the metalsubstrate, and the silane coated metal (without a polymer layer) may beexposed to the environment without significant deleterious effect. Thus,silane coatings provided by the unhydrolyzed silane compositions of thepresent invention provide a high level of corrosion protection evenwithout a polymer layer thereon, and will still provide improved polymeradhesion even after a lengthy exposure to the environment.

EXAMPLES Hydrolyzed Silane Solutions

The examples below demonstrate some of the superior and unexpectedresults obtained by employing the methods of the present invention.Unless otherwise noted, the various silane solutions described in thefollowing examples were prepared by mixing the indicated silane(s) withwater, solvent (ethanol), and acetic acid (if needed to provide theindicated pH during solution preparation). In instances wherein both abis-silyl aminosilane and a bis-silyl polysulfur silane were employed,the silanes were hydrolyzed separately in a solution of water andsolvent, and the hydrolyzed silane solutions were then mixed to form thefinal silane solution composition indicated. The individual silanesolutions were hydrolyzed for at least 24 hours prior to application.The metal substrates were solvent-cleaned, alkaline-cleaned, waterrinsed, dried, dipped into the silane solution for approximately 1minute, and then dried at room temperature.

In most of the rubber bonding tests which follow, three types ofsulfur-cured rubber formulations were used: (1) a typical tire-cord skimcompound having a cobalt adhesion promoter; (2) a typical tire-cord skimcompound without cobalt adhesion promoter; and (3) a low-sulfur compoundused, for example, in engine mount applications. The formulationsemployed are set forth below (in parts by weight).

Rubber Formulations Compound 1 Compound 2 Compound 3 NatSyn rubber 100.0100.0 — Natural rubber (SMR-5) — — 100.0 Zinc Oxide  10.0  10.0  3.0Stearic acid  1.2  1.2  2.0 Carbon black  60.0  60.0  50.0 (N326) (N326)(N330) Santoflex 13  1.0  1.0  2.0 Sundex 790 — —  10.0 Cobaltnaphthenate 10%  2.0 — — Vulkacit DZ  0.5  0.5 — PVI  0.2  0.2 —Insoluble sulfur (20% oil)  7.0  7.0 — Microcrystalline wax — —  2.0 CBS— —  1.4 Sulfur — —  2.5

Example 1

The following table provides adhesion results using hydrolyzed silanesolutions on cold rolled steel (“CRS”). For each of the silanesolutions, the indicated concentration (by volume) of the silane wasmixed with alcohol (methanol or ethanol) and an amount of waterequivalent to the silane concentration. For example, a 5% A1170 solutionwas prepared by mixing 5% A1170, 5% water and 90% ethanol (by volume).The pH was adjusted to the indicated amount by adding acetic acid asneeded. The silane solution was stirred for at least 24 hours in orderto complete hydrolysis. For mixtures of A1170 and A1289, the silaneswere separately hydrolyzed in the same manner (5% silane, 5% water and90% alcohol). After at least 24 hours of hydrolysis, the two silanesolutions were mixed together to provide the indicated ratio ofA1170:A1289, with the total silane concentration in the mixed silanesolutions being 5% in all cases.

CRS panels were ultrasonically cleaned in acetone, hexane and methanol.The panels were then alkaline cleaned in the usual manner, rinsed indeionized water, and blow-dried with hot air. The panels were thendipped into the silane solution for 30-45 seconds, and thereafter dried.

In order to evaluate the adhesion to rubber provided by the silanecoatings, a layer of the specified uncured rubber composition wassandwiched between two silane coated panels. One half of each metalpanel was shielded from the rubber by a Mylar film in order to preventbonding in that region. The composite article was then cured in ahydraulic press at 160° C. (8 minutes for Rubber Compound 1, 11 minutesfor Rubber Compound 2, and 5 minutes for Rubber Compound 3). Aftercuring, adhesion strength was measured by pulling portion of each metalpanel not bonded to the cured rubber (because of the Mylar film) awayfrom the rubber in opposite directions using an Instron Tensile Tester(Instron 4465) at a jaw speed of 2.54 cm/min. The force required toseparate the composite is shown in the table, along with the failuremode. A “100% interface” failure mode means that the metal peeled awayfrom the rubber, while “cohesive failure” means that the rubber itselffailed before the metal to rubber bond.

Silane, Rubber Failure Conc. pH compound Instron mode None — Compound 20 N 100% Interface VS, 5% 4.0 Compound 2 0 N 100% Interface BTSE, 5% 4.0Compound 2 0 N 100% Interface 2% BTSE, 4.0 Compound 2 0 N 100% 5% VS**Interface A1170, 5% 4.0 Compound 2 0 N 100% Interface A1289, 2% 7.9Compound 2 122 ± 43 N 100% Interface A1289, 2% 2.9 Compound 2  160 ± 150N 100% Interface A1259, 2% 5.0 Compound 2 115 ± 50 N 100% InterfaceA1289, 1% 6.5 Compound 2 120 ± 79 N 100% Interface A1289, 0.5% 6.0Compound 2 174 ± 15 N 100% Interface A1289, 5% 4.0 Compound 2 350 ± 20 N100% Interface A1170:A1289 = 3:1 6.9 Compound 2 233 ± 20 N 100%Interface A1170:A1289 = 3:1 4.4 Compound 2 161 ± 88 N 100% InterfaceA1170:A1289 = 1:1  6.95 Compound 2 262 ± 13 N 100% Interface A1170:A1289= 1:1 4.5 Compound 2 272 ± 18 N 100% Interface A1170:A1289 = 1:3 7.1Compound 2 264 ± 57 N 100% Interface A1170:A1289 = 1:3 4.4 Compound 2692 ± 50 N >80% Cohesive A1170:A1289 = 1:3 4.4 Compound 2 220 ± 78 N 50%Cohesive A1170:A1289= 1:3* 4.2 Compound 2 238 ± 31 N 100% InterfaceA1170:A1289 = 1:9 4.4 Compound 2 438 ± 57 N 50% Cohesive A1170:A1289 =1:9 4.4 Compound 2 179 ± 18 N 100% Interface A1170:A1289 = 1:4 4.2Compound 2 327 ± 16 N 50% Cohesive A1170:A1289 =  4.38 Compound 2 184 ±10 N 100% 1:19 Interface A1289, 2% 6.5 Compound 1 212 ± 30 N 100%Interface A1289, 5% 6.5 Compound 1 267 ± 30 N 100% Interface A1170:A1289= 1:3  4.25 Compound 1 215 ± 11 N 100% Interface A1170:A1289 = 1:3 4.4Compound 3 271 ± 7 N  100% Interface A1170:A1289 = 1:9 4.4 Compound 3246 ± 17 N 100% Interface A1170:A1289 = 4.2 Compound 3 257 ± 60 N 100%1:19 Interface *A-1170 solution was one week old **two-step treatmentmethod VS = vinyltrimethoxysilane BTSE = 1,2-bis-(triethoxysilyl)ethaneA-1170 bis-(trimethoxysilylpropyl) amine A-1289 =bis-(triethoxysilylpropyl) tetrasulfide

The wide discrepancies in the data reported above are due, in part, tothe nature of the method of measuring adhesion. For example, many of thesamples bent during testing, thereby calling into question the accuracyof adhesion force measurements for such samples. Therefore, the mode offailure provides a more accurate representation of rubber adhesion.

As indicated by the above results, mixtures of hydrolyzed A1170 andA1289 provided adhesion which was surprisingly superior to that providedby either silane alone. In fact, a hydrolyzed solution of A1170 providedno adhesion at all, yet even a small addition of A1170 to a hydrolyzedsolution of A1289 improves adhesion. Other hydrolyzed silane solutionsprovided no adhesion to the sulfur-cured rubber, including the two-stepBTSE/VS treatment which has previously been shown to provide excellentadhesion to peroxide-cured rubbers. The above results also indicate thatthe hydrolyzed silane mixtures of the present invention allow for theelimination of cobalt adhesion promoters, since the silane mixtures ofthe present invention provide better adhesion when the cobalt adhesionpromoter is not used.

Example 2

Panels of electrogalvanized (“EGS”) were tested in the same manner as inExample 1, and the results are provided below.

Silane, Rubber Failure Conc. pH compound Instron mode A1170, 5% 8.5Compound 2 0 N 100% Interface A1289, 5% 6.5 Compound 2 120 ± 30 N 100%Interface A1170:A1289 = 3:1 6.9 Compound 2 121 ± 61 N 100% InterfaceA1170:A1289 = 1:1 6.9 Compound 2  91 ± 13 N 100% Interface A1170:A1259 =1:3 7.1 Compound 2  72 ± 35 N 100% Interface

As noted from the above table, the addition of hydrolyzed A1170 tohydrolyzed A1289 solutions does not significantly affect adhesionperformance, even though hydrolyzed A1170 by itself provides noadhesion. However, the addition of A1170 during the period of time willprovide greater corrosion protection, particularly during metal shipmentor storage between application of the silane coating and rubber bonding.

Example 3

Panels of tin-coated CRS were tested in the same manner as in Example 1,and the results are provided below.

Silane, Rubber Failure Conc. pH compound Instron mode A1170:A1289 = 1:3 4.25 Compound 1 227 ± 18 N 100% Interface A1170:A1289 = 1:9 4.4Compound 1 173 ± 44 N 100% Interface A1170:A1289 =  4.38 Compound 1 164± 4 N  100% 1:19 Interface

Unhydrolyzed Silanes

In the next set of examples, unhydrolyzed silane compositions wereemployed. Unless otherwise noted, all of the silane coatings wereapplied from pure silanes (either pure A1170, or a mixture consistingonly of A1170 and A1289 in the indicated ratio). After the silanes weremixed with one another, the resultant silane mixture was wiped onto themetal (which had been cleaned in the manner described previously) usinga paper towel. Unless otherwise noted, the silane coating applied inthis manner was then dried for one hour at 150° C. Thereafter, therubber composition was bonded to the silane coated metal in the mannerdescribed previously.

Example 4

Panels of 63/37 brass were coated with unhydrolyzed silanes, and rubberadhesion was tested in the same manner as in Example 1:

Silane, Rubber Failure Conc. compound Instron mode Blank Compound 1 800± 50 N 100% Cohesive A1170:A1289 = 1:3 Compound 1 685 ± 81 N 75%Cohesive Blank Compound 2 450 ± 30 N 60% Cohesive A1170:A1289 = 1:3Compound 2 926 ± 71 N 90% Cohesive Blank Compound 3 380 ± 33 N 100%interface A1170:A1289 = 1:3 Compound 3 679 ± 49 N 70% Cohesive

Although sulfur-cured rubber having a cobalt adhesion promoter adhereswell to uncoated 63/37 brass, the unhydrolyzed A1170/A1289 mixtureprovided excellent adhesion to all three rubber formulations (with orwithout the cobalt adhesion promoter). Thus, the silane mixtures of thepresent invention allows for the elimination of the cobalt adhesionpromoter, while also providing improved corrosion protection.

Example 5

Panels of Alloy 360 brass and Alloy 260 brass were coated withunhydrolyzed silanes, and adhered to a rubber composition in the samemanner as in Example 4. Rubber adhesion was then tested in accordancewith ASTM D429(B), and the results are provided below.

Rubber Metal Silane, Conc. compound Adhesion Alloy 360 brass BlankCompound 1 0 N/mm Blank Compound 2 0 N/mm A1170:A1289 = 1:3 Compound 210.46 ± 1.6 N/mm Alloy 260 brass Blank Compound 1 12.13 ± 3.0 N/mm BlankCompound 2 10.23 ± 3.6 N/mm A1170:A1289 = 1:3 Compound 2 11.14 ± 1.4N/mm

As the above table indicates, the unhydrolyzed silane mixtures of thepresent invention provide excellent rubber adhesion on a variety ofbrass alloys, including Alloy 360 brass (which will not adhere tosulfur-cured rubber).

Example 6

Panels of CRS were coated with unhydrolyzed silanes, and rubber adhesionwas tested in the same manner as in Example 4:

Silane, Rubber Failure Conc. compound Instron mode Blank Compound 2 0 N100% Interface A1170:A1289 = 1:3* Compound 2 325 ± 36 N  10% CohesiveA1170:A1289 = 1:3** Compound 2 752 ± 124 N 2 samples ≈ 80% cohesivefailure, 1 sample ≈ 50% cohesive failure A1170:A1289 = 1:3** Compound 2476 ± 296 N 1 sample ≈ 80% cohesive failure, 2 samples ≈ 30% cohesivefailure A1170:A1289 = 1:1* Compound 2 284 ± 34 N  10% CohesiveA1170:A1289 = 1:1** Compound 2 398 ± 163 N ≈20% cohesive failureA1170:A1289 = 1:1** Compound 2 261 ± 39 N  10% cohesive failure BlankCompound 3 0 N 100% Interface A1170:A1289 = 1:3** Compound 3 209 ± 29 N 100% Interface *silane mixture had aged for 2 days **silane mixture hadaged for one week

Once again the large discrepancies in the adhesion values noted in theabove table are due, in part, to the nature of the test employed.Therefore, the mode of failure is considered by the Applicants to bemore significant. The above results demonstrate that unhydrolyzedmixtures of A1170 and A1289 provide even greater rubber adhesion thanthe hydrolyzed silane solutions of the present invention. This issurprising since conventional wisdom teaches that silanes should beapplied to metals in a hydrolyzed state, rather than substantiallyunhydrolyzed. In addition, applicants have found that while unhydrolyzedA1289 alone will not form a dry film, when combined with unhydrolyzedA1170 it provides a superior, crosslinked silane coating. This highlycrosslinked silane coating not only provides improved adhesion torubbers and other polymers (such as paint), it also provides excellentcorrosion protection (even without a polymer layer on top of the silanecoating).

Example 7

Panels of EGS were coated with unhydrolyzed silanes, and rubber adhesionwas tested in the same manner as in Example 4:

Silane, Rubber Failure Conc. compound Instron mode Blank Compound 2 0 N100% Interface A1170:A1289 = 1:3* Compound 2 567 ± 200 N 2 samples ≈ 80%cohesive failure, 1 sample ≈ 30% cohesive failure A1170:A1289 = 1:3**Compound 2 629 ± 132 N 1 sample ≈ 80% cohesive failure, 2 samples ≈ 40%cohesive failure A1170:A1289 = 1:3** Compound 2 422 ± 73 N  20% cohesivefailure A1170:A1289 = 1:1* Compound 2 640 ± 70 N  85-90% cohesiveA1170:A1289 = 1:1** Compound 2 606 ± 124 N ≈40-50% cohesive failureA1170:A1289 = 1:1** Compound 2 433 ± 245 N 1 sample ≈ 80% cohesivefailure, 2 samples ≈ 20% cohesive failure Blank Compound 3 0 N 100%Interface A1170:A1289 = 1:3** Compound 3 534 ± 157 N 2 sample ≈ 60%cohesive failure, 1 sample ≈ 40% cohesive failure A1170:A1289 = 1:1**Compound 3 391 ± 135 N ≈30% cohesive failure *silane mixture had agedfor 2 days **silane mixture had aged for one week

Example 8

Panels of NedZinc (a zinc-titanium alloy) were coated with unhydrolyzedVilanes, and rubber adhesion was tested in the same manner as in Example4:

Silane, Rubber Failure Conc. compound Instron mode A1170:A1289 = 1:3*Compound 2 434 ± 131 N 50% cohesive failure *silane mixture had aged for2 days

Example 9

In order to evaluate the stability of aluminum to rubber bonding usingunhydrolyzed silanes, panels of aluminum were coated with unhydrolyzedsilanes. SBR, NBR and EPDM rubber compositions were used in this test,and the rubber formulations were as follows:

SBR NBR SBR 1500 100.0 — NBR — 100.0 Zinc Oxide  5.0  5.0 Stearic acid 2.0  2.0 Processing Aid  4.0 — DOP —  10.0 Carbon black 50.0  30.0(N330) (N770)  70.0 (N550) MBTS  1.0 — TMTD  0.5  2.0 Sulfur  2.0  1.5CBS —  1.0

EPDM 1 EPDM 2 Vistalon 2504 100.0 — Vistalon — 50.0/50.0 5630/5300 ZincOxide  5.0  5.0 Stearic acid  1.0  1.0 Aromatic Oil  35.0 — NaphthenicOil —  60.0 Carbon black  60.0  75.0 (N990) (N990)  70.0  75.0 (N550)(N550) TMTD  0.6  2.0 MBTS  1.0 — CBS —  2.0 ZDBC  2.0 — DTDM —  2.0Sulfur  2.0  0.3

The cured rubber compositions were applied to silane coated panels, andthen cured by standard curing conditions. Rubber adhesion was testedaccording to ISO 813 (equivalent to ASTM D429B), and was reportedqualitatively. The panels were tested immediately after curing, andafter the specified exposure time in water at 100° C.

Rubber Exposure Time in Water, 100° C. Silane, Conc. compound Initial 24hr 48 hr 72 hr 168 hr A1170:A1289 = 1:3 EPDM 1 3.8 3.5 3.5 3.5 3.5A1170:A1289 = 1:3 EPDM 2 3.5 3.4 3.4 3.4 3.0 A1170:A1289 = 1:3 SBR 4  4   3.8 3.8 3.8 A1170:A1289 = 1:3 NBR 4   4   4   4   4   4 = ≧95%rubber (i.e., cohesive) failure 3 = high strength, partial rupture, >10%rubber failure 2 = medium strength peel - interfacial rupture 1 = lowstrength peel 0 = no bond

Example 10

Various other metals were adhered to rubber in the same manner asExample 9, using a mixture of unhydrolyzed A1170 and unhydrolyzed A1289(1:3 ratio). Rubber adhesion was evaluated according to ISO 813, and theadhesion results are reported below (in N/mm).

Rubber Exposure Time in Water, 100° C. Metal compound Initial 72 hrs 168hrs 336 hrs 304 Stainless Steel EPDM 1 6.1 7.1 6.1 N/mm 8.0 8.5 8.1 1010Carbon Steel EPDM 1 8.3 6.0 7.4 6.3 5.1 4.9 Aluminum EPDM 1 5.3 5.9 6.170/30 Brass EPDM 1 7.9 6.5 6.8 304 Stainless Steel NBR 12.9  9.9 11.4 1010 Carbon Steel NBR 14.6  10.4  15.3  Aluminum NBR 8.6 7.8 10.4  70/30Brass NBR 15.1  9.4 8.7 304 Stainless Steel EPDM 3 8.9 8.5 5.6 1010Carbon Steel NBR 2 20.6  10.3  9.4

“EPDM 3” and “NBR 2” were standard peroxide-cured EPDM and NBR rubbers,respectively.

Example 11

In order to examine the effect of silane aging, low carbon steel (SAEC-1018) was bonded to rubber in the same manner as in Example 10(unhydrolyzed silanes, A1170:A1289=1:3). Rubber adhesion was also testedin accordance with ASTM D429B.

Age of Silane Mixture Peel Strength, N/mm Mode of Failure Fresh 11.7 ±1.5 100% cohesive Aged 2.5 weeks 11.2 ± 1.3 100% cohesive Aged 8 weeks13.0 ± 0.8 100% cohesive

Example 12

In order to examine the effect of silane concentration in theunhydrolyzed systems of the present invention, CRS was bonded to rubberin the same manner as in Example 10 (unhydrolyzed silanes,A1170:A1289=1:3). Rubber adhesion was also tested in the same manner asin Example 11.

Rubber Adhesion Failure Silane, Conc. compound Strength mode 100%Silanes Compound 2 11.7 ± 1.5 N/mm 100% Cohesive (A1170:A1289 = 1:3) 50%Silanes in Compound 2  9.5 ± 1.7 N/mm 100% Cohesive Ethanol 25% Silanesin Compound 2 10.4 ± 4.4 N/mm 90% Cohesive Ethanol 100% Silanes Compound3 10.2 ± 2.3 N/mm 80% Cohesive (A1170:A1289 = 1:3)

As noted above, the unhydrolyzed silane mixtures of the presentinvention may be applied as pure silanes (i.e., no solvents), or withsignificant quantities of non-aqueous solvents (such as ethanol ormethanol).

Comparison of Corrosion Protection Provided by Hydrolyzed andUnhydrolyzed Silanes Example 13

In order to examine the corrosion protection provided by the hydrolyzedand unhydrolyzed silane compositions of the present invention, silanecoatings were applied to pure aluminum panels. The hydrolyzed silanesolutions were prepared and applied in the manner described in Example1, and the unhydrolyzed silanes were prepared and applied as describedin Example 4. The silane coated panels were then placed into a 3% NaClsolution for 192 hours. Corrosion was evaluated qualitatively, and theresults are shown below.

Curing Silane Solution pH Conditions Surface Observation Blank N/A —large size pits, distributed uniformly A1170, hydrolyzed, 5% 8 dried atroom small pits, distributed solution temperature uniformly A1289,hydrolyzed, 5% 8 dried at room almost original solution temperatureappearance 5% A1170 + 5% A1289, 8 dried at room almost originalhydrolyzed temperature appearance pure A1170, N/A 160° C. for 30original appearance unhydrolyzed minutes 1:1 mixture of A1170 N/A 160°C. for 30 almost original and A1289, minutes appearance unhydrolyzed (nosolvent)

As shown in the above table, the mixture of hydrolyzed A1170 and A1289provided excellent corrosion protection (superior to hydrolyzed A1170alone, and at least equivalent to hydrolyzed A1289 alone). Theunhydrolyzed silanes (including pure A1170, as well as the A1170/A1289mixture) also provided excellent corrosion prevention. Thus, the silanesolutions and methods of the present invention not only provide superiorpolymer adhesion, but also provide corrosion protection (with or withouta polymer layer over the silane coating).

The corrosion protection provided by the methods of the presentinvention on CRS and EGS was also measured quantitatively by conductingstandard electrochemical polarization tests. The results of these testsare shown below, wherein the rate of corrosion is reported inmillimeters per year.

What we claim is:
 1. A method of treating a metal substrate, comprising:(a) providing a metal substrate; (b) applying a coating of a silanecomposition onto the metal substrate, said silane composition comprisingat least one substantially unhydrolyzed aminosilane which has one ormore secondary or tertiary amino groups; and (c) adhering a polymerlayer to said coating.
 2. The method of claim 1, wherein said polymerlayer comprises rubber.
 3. The method of claim 2, wherein said polymerlayer comprises a sulfur-cured rubber.
 4. A method of treating a metalsubstrate, comprising: (a) providing a metal substrate; (b) applying acoating of a silane composition onto the metal substrate, said silanecomposition comprising at least one substantially unhydrolyzedaminosilane which has one or more secondary or tertiary amino groups,wherein said aminosilane comprises a bis-silyl aminosilane having twotrisubstituted silyl groups, wherein the substituents are individuallychosen from the group consisting of alkoxy, aryloxy and acyloxy; andwherein the silane composition further comprises at least onesubstantially unhydrolyzed bis-silyl polysulfur silane; and (c) adheringa polymer layer to said coating.
 5. The method of claim 4, wherein saidpolymer layer comprises rubber.
 6. The method of claim 4, wherein saidpolymer layer comprises a sulfur-cured rubber.
 7. A method of adheringrubber to a metal substrate, comprising: (a) applying a coating of asilane composition onto a metal substrate, said silane compositioncomprising: a bis-silyl aminosilane, or the hydrolysate or partialhydrolysate thereof; and a bis-silyl polysulfur silane, or thehydrolysate or partial hydrolysate thereof; and (b) adhering rubber tosaid coating.
 8. The method of claim 7, wherein said bis-silylaminosilane comprises an aminosilane having two trisubstituted silylgroups, wherein the substituents are individually chosen from the groupconsisting of alkoxy, aryloxy and acyloxy.
 9. The method of claim 8,wherein said bis-silyl aminosilane comprises:

wherein: each R¹ is individually chosen from the group consisting of:C₁-C₂₄ alkyl and C₂-C₂₄ acyl; each R² is individually chosen from thegroup consisting of: substituted aliphatic groups, unsubstitutedaliphatic groups, substituted aromatic groups, and unsubstitutedaromatic groups; and X is either:

wherein each R³ is individually chosen from the group consisting of:hydrogen, substituted and unsubstituted aliphatic groups, andsubstituted and unsubstituted aromatic groups; and R⁴ is chosen from thegroup consisting of: substituted and unsubstituted aliphatic groups, andsubstituted and unsubstituted aromatic groups.
 10. The method of claim9, wherein each R¹ is individually chosen from the group consisting of:ethyl, methyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl,ter-butyl and acetyl.
 11. The method of claim 9, wherein X is chosenfrom the group consisting of: a C—Si bond, C₁-C₆ alkylene, C₁-C₆alkenylene, C₁-C₆ alkylene substituted with at least one amino group,C₁-C₆ alkenylene substituted with at least one amino group, arylene, andalkylarylene.
 12. The method of claim 9, wherein each R² is individuallychosen from the group consisting of: hydrogen, ethyl, methyl, propyl,iso-propyl, butyl, iso-butyl, sec-butyl, ter-butyl and acetyl.
 13. Themethod of claim 7, wherein said bis-silyl aminosilane is chosen from thegroup consisting of: bis-(trimethoxysilylpropyl)amine,bis-(triethoxysilylpropyl)amine, and bis-(triethoxysilylpropyl)ethylenediamine.
 14. The method of claim 7, wherein said bis-silyl polysulfursilane comprises:

wherein each R¹ is an alkyl or an acetyl group, and Z is —Q—S_(x)—Q—,wherein each Q is an aliphatic or aromatic group, and x is an integer offrom 2 to
 10. 15. The method of claim 14, wherein each R¹ isindividually chosen from the group consisting of: ethyl, methyl, propyl,iso-propyl, butyl, iso-butyl, sec-butyl, ter-butyl and acetyl.
 16. Themethod of claim 14, wherein each Q is individually chosen from the groupconsisting of: C₁-C₆ alkyl (linear or branched), C₁-C₆ alkenyl (linearor branched), C₁-C₆ alkyl substituted with one or more amino groups,C₁-C₆ alkenyl substituted with one or more amino groups, benzyl, andbenzyl substituted with C₁-C₆ alkyl.
 17. The method of claim 7, whereinsaid at least one bis-silyl polysulfur silane comprises abis-(triethoxysilylpropyl) sulfide having 2 to 10 sulfur atoms.
 18. Themethod of claim 17, wherein said at least one bis-silyl polysulfursilane comprises bis-(triethoxysilylpropyl)tetrasulfide.
 19. The methodof claim 7, wherein said metal substrate is chosen from the groupconsisting of: zinc and zinc alloys; metal substrates having azinc-containing coating; steel; aluminum and aluminum alloys; copper andcopper alloys; tin and tin alloys; and metal substrates havingtin-containing coatings.
 20. The method of claim 7, wherein the silanesin said silane composition are substantially unhydrolyzed.
 21. Themethod of claim 20, wherein the ratio of bis-silyl aminosilanes tobis-silyl polysulfur silanes in said silane composition is between about1:10 and about 10:1.
 22. The method of claim 20, wherein said silanecomposition further comprises a non-aqueous solvent.
 23. The method ofclaim 7, wherein said silane composition consists essentially of said atleast one substantially unhydrolyzed bis-silyl aminosilane and said atleast one substantially unhydrolyzed bis-silyl polysulfur silane. 24.The method of claim 7, wherein the silanes in said silane compositionare at least partially hydrolyzed.
 25. The method of claim 24, whereinthe ratio of bis-silyl aminosilanes to bis-silyl polysulfur silanes insaid silane composition is between about 1:10 and about 10:1.
 26. Themethod of claim 25, wherein said silane composition further compriseswater and a solvent.
 27. The method of claim 26, wherein the ratio ofwater to solvent in said silane composition is between about 1:1 andabout 1:20.
 28. The method of claim 24, wherein the pH of said silanecomposition is between about 4 and about
 7. 29. The method of claim 7,wherein said rubber comprises a sulfur-cured rubber.
 30. The method ofclaim 29, wherein said step of adhering said sulfur-cured rubbercomprises applying an uncured rubber compound directly onto said silanecoating, and thereafter curing said rubber compound.
 31. The method ofclaim 30, further comprising the step of drying said silane coatingprior to applying said uncured rubber compound.
 32. A metal substratehaving a polymer layer thereon, made in accordance with the method ofclaim
 1. 33. A metal substrate having rubber adhered thereto made inaccordance with the method of claim 7.